They didn't do anything to cause women to cheat on them. Someone who cheats is always the one at fault there, because it's a choice.

They may have done anything to cause their exes to be unhappy in the relationship. Or not. But they didn't cause their exes to cheat, the exes made that choice instead of being more respectful and ending the relationship.

Blaming the victim? That's never ok.

As to whether it's a line or not? You'll never know if you don't trust them. But it isn't always a line and it isn't always the truth. It depends on the person. Men get cheated on just the same as women get cheated on, so statistically there are certainly men who are telling the truth about having been cheated on.